class_docstr: Interface for implementing a Trial Scheduler class.
  
  Note to Tune developers: If a new scheduler is added, please update
  `air/_internal/usage.py`.
docstr: Called when a new trial is added to the trial runner.
docstr_tok: ["Called","when","a","new","trial","is","added","to","the","trial","runner","."]
code: def on_trial_add(
      self, tune_controller: "TuneController", trial: Trial
  ):
      """Called when a new trial is added to the trial runner."""
  
      raise NotImplementedError
  
imports: from typing import Dict, Optional, TYPE_CHECKING
  from ray.air._internal.usage import tag_scheduler
  from ray.tune.result import DEFAULT_METRIC
  from ray.tune.experiment import Trial
  from ray.util.annotations import DeveloperAPI, PublicAPI
label_desc: Use image node_id 5 for calling the TrialScheduler obj's underlying member method code with example usage: obj.on_trial_add(tune_controller, trial) without return types